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the
Always use a free tape: For each full backup
option is selected
the
Always use a free tape: For each incremental backup
option is selected
the
Always use a free tape: For each differential backup
option is selected.
The figure shows tape rotation for the ToH scheme with these options.
Maximal number of tapes used in the rotation is seven that is more than in classical five-level ToH
scheme.
Two additional tapes used for:
1.
keeping an old full backup (postponed deletion) as it is a base for other level backups
2.
keeping an old backup on a level until a new backup has been successfully created on the level.
The example demonstrates that the tapes’ usage efficiency is reduced. Moreover, the data recovery
requires access to the backups kept on one (full backups, 6%), two (differential backups, 44%) or
three (incremental backups, 50%) tapes. So on average the operation takes more time than in the
previous examples.
Tape planning
Once you have specified the backup scheme and tape options, you should determine the minimal
number of tapes necessary to achieve full automation of tape rotation.
To simplify the tape planning lets discard the possibility that the calculated tapes might contain
backups of other data. It is implied that the
Use a separate tape set
option is enabled.
To calculate the number of tapes you should take into account the following considerations:
full backup size
average size of incremental backups
average size of differential backups
